A conventional disc package capable of storing therein a plurality of discs includes a base on which the plurality of discs are stacked, a bucket-shaped cover for covering the discs mounted on the base, and a male screw cap for fixing the cover on the base.
Installed at the center of a top surface of the base is a shaft to be inserted through a center hole of each disc. Formed on an upper end portion of the shaft is a female screw hole corresponding to the screw of the cap. The cover has a screw-through hole formed on a center portion of the upper surface thereof.
A disc packaging process using the above-described disc package is provided as follows. The shaft is inserted through a center hole of each disc, so that the discs are stacked on the base. Then, the discs stacked on the base are covered with the cover, and the screw of the cap is inserted into the female screw hole of the shaft through the screw-through hole, thereby firmly fixing the cover on the base.
In the disc package described above, a troublesome screwing operation is required in order to fix the cover on the base. Accordingly, the costs for the disc packaging are increased.
Another conventional disc package includes a base for stacking thereon the plurality of discs and a bucket-shaped cover for covering the discs mounted on the base. In such a disc package, the cover is pressurized onto the base along a shaft axial direction to be mounted thereon. A disc package of this type is disclosed in Japanese Utility Model Application No. 2-125170 (Japanese Utility Model Laid-Open Publication No. 4-84189).
In such a disc package described in FIG. 7, the cover can be mounted on the base simply by being pressurized onto the base along the shaft axial direction. However, since a locking structure for locking the cover onto the base is not provided, the cover mounted on the base may be separated therefrom due to vibrations while the disc package is being transported.
Meanwhile, in such a disc package described in FIGS. 1 to 6, a cover and a base are formed in such a manner that they cannot be connected to and separated from each other unless the cover is rotated along the circumference of the base. Further, since a locking structure is prepared, the cover once fixed on the base can be prevented from being separated therefrom due to vibrations while the disc package is being transported. However, the disc package has a disadvantage in that the cover cannot be fastened to the base simply by being pressurized onto the base. Further, the cover cannot be mounted on the base unless it is precisely aligned along the circumference of the base. Moreover, the cover should be rotated only in a predetermined direction, i.e., either in a clockwise or a counterclockwise direction, to be separated from the base. If the cover is rotated in a reverse direction, it becomes impossible to separate the cover from the base.
Therefore, Japanese Utility Model Laid-Open Publication No. 4-84189 does not provide a disc package capable of allowing a cover to be fixed on a base simply by pressurizing the cover along a shaft axial direction with a locking mechanism for securely fixing the cover on the base.
Still another conventional disc package has a disc-shaped base for stacking thereon discs and a bucket-shaped cover for covering the discs mounted on the base, wherein protruded portions are disposed at the circumference of either the base or the cover, and coupling grooves to be coupled with the protruded portions are provided at the corresponding circumference. Such an example is disclosed in Japanese Patent Laid-Open Publication No. 2000-168872.
In such a disc package, when one end portion of the coupling groove extending along a circumferential direction of the cover faces to the protruded portion, a user can recognize that the cover can be separated from the base along the shaft axial direction. On the other hand, when the other end portion of the coupling groove faces to the protruded portion, a user can recognize that the cover cannot be separated from the base along the above-described direction.
Though not shown in FIGS. 7 and 8, when the cover is mounted on the base by being pressurized thereonto along the shaft axial direction, it is preferable to extend a circumferential length of the coupling groove as much as possible in order to precisely align the protruded portion with the groove. In other words, the best way to align is to form the coupling groove all around the circumference of the base or the bucket-shaped cover. In this case, the protruded portion can be more precisely aligned with the coupling groove in the process of mounting the cover on the base, but the protruded portion cannot be faced with the end portion of the coupling groove. Therefore, a user cannot recognize whether or not the cover can be separated from the base along the shaft axial direction. Further, in this case, the cover cannot be separated from the base in a conventional way.
Still another conventional disc package includes a disc-shaped base for stacking thereon discs and a shaft for aligning a plurality of stacked discs on the base, wherein the base and the shaft are manufactured as one body. In this case, a process for assembling the base and the shaft can be omitted. However, since they cannot be separated from each other even while being transported, transportation costs become increased.
In the meantime, there is a conventional disc package having a base and a shaft formed separately. In this case, it is required to assemble the base and the shaft. In such a disc package, the shaft is coupled to the base by using screws. An example is shown in Japanese Patent Laid-Open Publication No. 7-89585. Further, in another conventional disc package, a shaft is coupled to a base by performing, e.g., an ultrasonic welding. Such a disc package is disclosed in Japanese Patent Laid-Open Publication No. 11-349084. However, in case the shaft is installed on the base by using the two methods described above, assembly equipments are required and further, more time should be spent in assembly. As a result, an assembly cost becomes increased.
In order to prevent the assembly cost from being increased, there is provided a disc package in which a shaft is installed on a base by a snap fit. Specifically, a shaft is installed on the base with so-called an elastic pin using an elastic deformation of a portion of the shaft and made of resin. Such a disc package includes a flange contacting with a top surface of the base in order to make the shaft disposed vertically against the top surface of the base, and a coupling surface coupling to a bottom surface in order to prevent the shaft from being separated from the base. In this case, a distance between the flange and the coupling surface is larger than a thickness of the base located therebetween, so that the shaft can be installed on the base regardless of errors generated in manufacturing the base and the shaft. That is to say, there is provided a clearance between the distance and the thickness along the shaft axial direction. Further, for the same reason, a hole for mounting the shaft thereon, which is formed at the base, is larger than an external diameter of the shaft. In other words, there is also provided a clearance between the hole and the outer diameter along a shaft radial direction. As a result, since the shaft is shaken on the base, it is hard for the shaft to be vertically maintained against the top surface of the base. If the shaft is shaken and tilted, a merchantability of the disc package is decreased.
Still another conventional disc package includes a disc-shaped base for stacking discs thereon, a shaft for aligning a plurality of discs mounted on the base, a cover for covering the stacked discs and a concave portion formed at the cover in order to fit with an end portion of the shaft when the cover is mounted on the base. Such an example is disclosed in Japanese Patent Laid-Open Publication No. 2000-168872. In this disc package, grooves extending along a shaft axial direction are formed around a circumferential surface of the cover and protrusions are formed around a circumferential surface of the base. Further, when the cover is mounted on the base, a user needs to align the grooves with the protrusions to thereby fit the end portion of the shaft into the concave portion of the cover.
However, it is troublesome for a user to align the grooves with the protrusions. Therefore, it is preferable to mount the cover on the base by simply pressurizing the cover without the inconvenient aligning process.
In this case, however, if the cover is pressurized at a slight inclination angle onto the base, the end portion of the shaft and the concave portion of the cover may be misaligned. Especially, if the cover is made of a hard material, the end portion of the shaft will face with a peripheral portion of the concave portion. As a result, a user cannot pressurize the cover anymore, so that the end portion of the shaft and the concave portion cannot be coupled. Therefore, the cover cannot be mounted on the base.